Medical imaging technology has advanced to provide physicians with indispensable information on the macroscopic anatomy of patients. Imaging techniques such as radiography, magnetic resonance imaging, computed tomography and ultrasound allow investigations of large-scale structures in the human body in a non-invasive manner with resolutions ranging from 100 μm to 1 mm. However, many disease detection procedures and/or analysis, such as the detection of early stages of a particular cancer, require a higher resolution of imaging for an accurate diagnosis. In addition, clinical procedures (such as screening for carcinoma and detecting surgical tumor margins) require the implementation of higher resolution diagnostic imaging methods. To address these and other clinical problems, a non-invasive imaging technology, with a resolution that approaches standard histopathology, should be used in conjunction with an endoscope, borescope, catheter or the like.
A borescope, endoscope, or similar flexible probe can be generally incorporated in an elongated flexible insertion tube with a viewing head at its distal or forward end. A conventional borescope has a thin bendable tubular steering section (or articulation section) at the distal end thereof adjacent to the viewing head which is generally steered from a control housing. A conventional endoscope has a thin tubular probe with a viewing head at the distal end thereof. The viewing head for either the borescope or the endoscope can include optical components (e.g., fiber optic or video, components such as a CCD imager). This viewing head can be situated in the distal end of the articulation section of the borescope or the distal end of the thin tubular probe of the endoscope. A signal conduit or bundle (which can be a wire bundle in the case of a video device or a fiber optic bundle in the case of an optical device) passes from the head through the insertion tube to exit to a suitable viewing device. A fiber optic bundle can also be used to carry illumination to the viewing head for illuminating a target in an enclosed area.
For a number of years, confocal microscopy has been an important research tool for investigating the microstructure of excised specimens. Traditionally, the use of confocal microscopy has been limited to being applied to accessible surfaces of the skin and the eye. The reason for this is that the only reliable methods for optical scanning should be performed in free space. In addition, the size of optical scanners generally prohibit their use in small probes such as endoscopes, borescopes, catheters and the like.
A confocal microscope may consist of a point source of light, a beam splitter and a lens assembly. The light is transmitted through the beam splitter and the lens or lens assembly, and then imaged into a sample to form an illuminated spot or resolution element. Light remitted from the sample is redirected through the lens or lens assembly (if present), the beam splitter, and towards the detector. The detector aperture size is approximately matched to the illuminated spot size through the intermediate optics. This conventional arrangement prevents an out-of-focus light from entering the detector. Thus, the light returning from above, below or to the side of the point illumination within the sample is not detected, and the volume of the resolution element is defined in three-dimensions. With a high numerical aperture microscope objective, these sections can be very small, e.g., on the order of several micrometers.
For this conventional system, an extremely small spot is illuminated at any one time, therefore a coherent image should be built up by scanning point by point over the desired field of view, and recording the intensity of the light emitted at each spot. Such scanning can be accomplished in several ways, one of the more common systems is laser scanning.
A number of publications describe the subject matter which my be relevant to the microscope of the present invention. For example, U.S. Pat. No. 6,215,549 describes an optical anisotropy measuring apparatus utilizing the total internal reflection (“TIR”) method in the Background section thereof. As part of this TIR method, the refractive index matching liquid is filled between a liquid crystal device and each semispherical glass with the refractive index matching liquid having generally the same refractive index as the glass substrate and semispherical glass.
U.S. Pat. No. 6,019,472 describes a multi-layered contact lens element for at least one of examination and treatment of ocular tissues. The lenses used in the multi-layered contact lens element may be composed of various industry materials including SF4, SF8 or LASFN31.
U.S. Pat. No. 5,808,813 discloses a variable-focus variable-magnification optical coupler for coupling an endoscope to a variety of different cameras. The optical coupler includes an adjustment mechanism which is actuated to move a focus lens assembly and a zoom lens assembly along the length of the optical coupler relative to a camera mount to focus the optical coupler.
U.S. Pat. No. 5,191,879 discloses a variable focus camera system for a borescope or endoscope. The lens cell of the system is free to move distally or proximally, thereby changing the focal length of the lens assembly. A vent is provided in a flexible sleeve of the assembly to allow air to be introduced to or taken from the volume which is altered when the lens cell moves distally or proximally.
U.S. Pat. No. 5,144,475 discloses an objective lens system to be used within a microscope. The objective lens system includes six (6) lenses which are spaced apart from an object side. The system includes a first to a fifth lens displaced in order from an object side to an image formation side with a predetermined number of air spacings therebetween. A first lens of this system is a meniscus lens, and has a concave surface directed toward an object. The first lens has the characteristics of an aplanat lens and a field flattener. Such objective lens system is a variation of an “Amici type” lens.
U.S. Pat. No. 5,123,743 discloses a method of detecting defects in a lithography mask. An optical microscope (with an immersion lens, a top lighting, and a bright field) is used to detect spots of chrome which indicate imperfections. A refractive index-matching oil, which contacts both the lens and the glass or other surface, eliminates reflections from the glass, so only light scattering or reflections from the spots of chrome are seen. The refractive index-matching oil has a refractive index substantially identical to that of the glass or other surface.
U.S. Pat. No. 5,119,117 discloses an objective lens system. This optical lens system includes a first lens group and a second lens group. The first lens group is positioned closer to the focal point than the second lens group and includes a single aplanat. The second lens group includes a chromatic doublet.
Japanese Patent Document No. JP10118007 discloses an endoscope with a focus adjustment system, which has an actuator drive circuit to drive a piezoelectric actuator that moves a lens for the focus adjustment. The piezoelectric actuator moves the lens along an optical axis in order to focus the system.